The invention relates to the art of sealing a leaky tube in a sheet-and-tube type heat exchanger through the detonation of explosive activated metal plugs inserted at both ends of the tube, and more particularly to an apparatus and method wherein distortion of the adjacent tubes and tube sheet ligaments by the explosive forces is substantially minimized.
Heat exchangers of the type to which this invention is especially applicable, are constructed with a large number of relatively small diameter tubes grouped in what is commonly referred to as a bundle. Heat is exchanged between a fluid passing through the tubes and a fluid in contact with the outside of the tubes. The fluids are physically separated by tubes and tube sheets, with one tube sheet being located at each end of the tube bundle. It is becoming common practice to seal off a leaky tube in this type of heat exchanger by employing an explosive activated plug in the form of a hollow metal body that is inserted at each end of the tube to be sealed. The plug contains a shaped explosive charge and a detonator which can be set off from a remote location to detonate the charge and thereby expand the plug body against the tube surface with an impact of sufficient force to weld the plug to the surrounding tube surface and form a fluid tight seal therebetween.
Some difficulty has been encountered with explosive welding in this type of heat exchanger where the closeness of the tubes is such that tubes adjacent to the leaky tube, and the tube sheet ligament therebetween may be significantly distorted by the explosive forces released during the detonation of a sealing plug in the leaky tube.